Faculty of Medicine, University of Geneva, Geneva, Switzerland.
J Transl Med. 2014 Jan 16;12:12. doi: 10.1186/1479-5876-12-12.
Magnetic Resonance-guided High Intensity Focused Ultrasound (MRgHIFU) is a hybrid technology that aims to offer non-invasive thermal ablation of targeted tumors or other pathological tissues. Acoustic aberrations and non-linear wave propagating effects may shift the focal point significantly away from the prescribed (or, theoretical) position. It is therefore mandatory to evaluate the spatial accuracy of ablation for a given HIFU protocol and/or device. We describe here a method for producing a user-defined ballistic target as an absolute reference marker for MRgHIFU ablations.
The investigated method is based on trapping a mixture of MR contrast agent and histology stain using radiofrequency (RF) ablation causing cell death and coagulation. A dedicated RF-electrode was used for the marker fixation as follows: a RF coagulation (4 W, 15 seconds) and injection of the mixture followed by a second RF coagulation. As a result, the contrast agent/stain is encapsulated in the intercellular space. Ultrasonography imaging was performed during the procedure, while high resolution T1w 3D VIBE MR acquisition was used right after to identify the position of the ballistic marker and hence the target tissue. For some cases, after the marker fixation procedure, HIFU volumetric ablations were produced by a phased-array HIFU platform. First ex vivo experiments were followed by in vivo investigation on four rabbits in thigh muscle and six pigs in liver, with follow-up at Day 7.
At the end of the procedure, no ultrasound indication of the marker's presence could be observed, while it was clearly visible under MR and could be conveniently used to prescribe the HIFU ablation, centered on the so-created target. The marker was identified at Day 7 after treatment, immediately after animal sacrifice, after 3 weeks of post-mortem formalin fixation and during histology analysis. Its size ranged between 2.5 and 4 mm.
Experimental validation of this new ballistic marker method was performed for liver MRgHIFU ablation, free of any side effects (e.g. no edema around the marker, no infection, no bleeding). The study suggests that the absolute reference marker had ultrasound conspicuity below the detection threshold, was irreversible, MR-compatible and MR-detectable, while also being a well-established histology staining technique.
磁共振引导高强度聚焦超声（MRgHIFU）是一种混合技术，旨在提供针对目标肿瘤或其他病理组织的非侵入性热消融。声波干扰和非线性波传播效应可能会导致焦点显著偏离预定（或理论）位置。因此，有必要评估给定 HIFU 方案和/或设备的消融空间准确性。我们在这里描述了一种用于产生用户定义的弹道目标的方法，作为 MRgHIFU 消融的绝对参考标记。
所研究的方法基于使用射频（RF）消融捕获包含磁共振对比剂和组织学染色剂的混合物，从而导致细胞死亡和凝固。专用的 RF 电极用于固定标记物，方法如下：进行 RF 凝固（4 W，15 秒）和混合物注射，然后进行第二次 RF 凝固。结果，对比剂/染色剂被包裹在细胞间隙中。在该过程中进行超声成像，然后立即进行高分辨率 T1w 3D VIBE MR 采集，以识别弹道标记物的位置，从而识别靶组织的位置。对于某些情况，在标记物固定程序之后，通过相控阵 HIFU 平台进行 HIFU 容积消融。首先进行了离体实验，然后在四只兔大腿肌肉和六只猪肝脏中进行了体内研究，并在第 7 天进行了随访。
在程序结束时，无法观察到标记物存在的超声迹象，而在 MR 下可以清晰可见，并可以方便地用于规定以创建的目标为中心的 HIFU 消融。在治疗后第 7 天，动物被处死时，在 3 周的尸体福尔马林固定后和进行组织学分析时，可以立即识别标记物。标记物的大小在 2.5 到 4 毫米之间。
这项新的弹道标记方法的实验验证是针对肝脏 MRgHIFU 消融进行的，没有任何副作用（例如标记物周围无水肿、无感染、无出血）。该研究表明，绝对参考标记物的超声可见性低于检测阈值，是不可逆的，与 MR 兼容且可检测，同时也是一种成熟的组织学染色技术。
